package easy;

/**
 * Created by daodao on 2018/7/16.
 * Problem 67
 * Description: Given two binary strings, return their sum (also a binary string).
 * The input strings are both non-empty and contains only characters 1 or 0.
 *
 * Example 1: Input: a = "11", b = "1"
 *            Output: "100"
 * Example 2: Input: a = "1010", b = "1011"
 *            Output: "10101"
 */
public class AddBinary {
    public static String addBinary(String a, String b) {
        StringBuilder binaryResult = new StringBuilder();
        int i = a.length() - 1, j = b.length() - 1;
        int carry = 0;
        while (i >= 0 || j >= 0) {
            int sum = carry;
            if (i >=0) {
                sum += a.charAt(i) - '0';
                i--;
            }
            if (j >= 0) {
                sum += b.charAt(j) - '0';
                j--;
            }
            if (sum >= 2) {
                binaryResult.append(sum % 2);
                carry = 1;
            } else {
                binaryResult.append(sum);
                carry = 0;
            }
        }
        if (carry == 1) {
            binaryResult.append(carry);
        }
        return binaryResult.reverse().toString();
    }
}
